Exposure apparatuses are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that retains a reticle, an optical assembly, a wafer stage assembly that retains a semiconductor wafer, and a measurement system. The semiconductor wafer includes a plurality of chip alignment marks that identify the location of the chips on the semiconductor wafer.
Typically, the wafer stage assembly includes a wafer stage base, a wafer stage including a wafer vacuum chuck that retains the wafer, and a wafer mover assembly that precisely positions the wafer stage and the wafer. Somewhat similarly, the reticle stage assembly includes a reticle stage base, a reticle stage that retains the reticle, and a reticle mover assembly that precisely positions the reticle stage and the reticle. In order to obtain precise relative positioning, the position of the reticle stage and the wafer stage are constantly monitored by the measurement system. Stated another way, the measurement system monitors movement of the device stage and the wafer stage relative to the optical assembly or some other reference. With this information, the wafer mover assembly can be used to precisely position the wafer and the reticle mover assembly can be used to precisely position the reticle.
As provided herein, the wafer mover assembly moves the wafer stage and the wafer between an alignment position and an operational position. In the alignment position, the wafer is loaded onto the wafer stage. Subsequently, in the alignment position, an alignment device, e.g. a microscope, is used to align and determine the position of the chip alignment marks of the wafer relative to the wafer stage and the measurement system. In the operational position, a projection device, e.g. a projection microscope, is used to check alignment of the wafer relative to the reticle through the optical assembly of the exposure apparatus. Finally, in the operational position, images from the reticle are transferred to the wafer.
The size of the images and features within the images transferred onto the wafer from the reticle are extremely small. Accordingly, the precise positioning of the wafer and the reticle relative to the optical device is critical to the manufacture of high density, semiconductor wafers.
One way to improve the accuracy of the exposure apparatus includes improving the determination of the location of the chip alignment marks relative to the wafer stage and the measurement system. For example, the alignment and determination of the chip alignment marks can be improved by (i) initially aligning and determining the position of the chip alignment marks in a first position with the alignment device, and (ii) subsequently, rotating the wafer 180 degrees to a rotated second position, and (iii) aligning and determining the position of the chip alignment marks in the second position with the alignment device. With this information, the errors in the alignment device can be averaged. Next, the wafer is rotated back to the first position and then the wafer is moved to the operational area.
Unfortunately, rotation of the wafer between the positions can deform the wafer. The deformation of the wafer compromises the accuracy of the alignment process. Further, the alignment process is compromised if the wafer is not rotated exactly between the positions. Ultimately, this reduces the accuracy of positioning of the wafer relative to the reticle and degrades the accuracy of the exposure apparatus.
In light of the above, there is a need for a wafer stage assembly and method for precisely rotating a device between a first position, a rotated second position and back to the first position without deforming, deflecting and/or distorting the device. Additionally, there is a need for a mover and method for accurately moving the wafer chuck relative to the wafer stage between the positions. Moreover, there is a need for a system and method for connecting the wafer chuck in fluid communication with a fluid source such as a vacuum source. Further, there is a need for an exposure apparatus that allows for more accurate positioning of the semiconductor wafer relative to the reticle. Furthermore, there is a need for an exposure apparatus capable of manufacturing precision devices such as high density, semiconductor wafers.